1. Field of the Invention
The present invention is related to magneto-fluidic acceleration sensors, and more particularly, to an acceleration sensor with a wide frequency response and a high dynamic range.
2. Background Art
Magneto-fluidic accelerometers are described in, e.g., U.S. patent application Ser. No. 10/836,624, filed May 3, 2004, U.S. patent application Ser. No. 10/836,186, filed May 3, 2004, U.S. patent application Ser. No. 10/422,170, filed May 21, 2003, U.S. patent application Ser. No. 10/209,197, filed Aug. 1, 2002 (now U.S. Pat. No. 6,731,268), U.S. patent application Ser. No. 09/511,831, filed Feb. 24, 2000 (now U.S. Pat. No. 6,466,200), and Russian patent application No. 99122838, filed Nov. 3, 1999. These accelerometers utilize magneto-fluidic principles and an inertial body suspended in a magnetic fluid, to measure acceleration. Such an accelerometer often includes a sensor casing (sensor housing, or “vessel”), which is filled with magnetic fluid. An inertial body (“inertial object”) is suspended in the magnetic fluid. The accelerometer usually includes a number of drive coils (power coils) generating a magnetic field in the magnetic fluid, and a number of measuring coils to detect changes in the magnetic field due to relative motion of the inertial body.
When the power coils are energized and generate a magnetic field, the magnetic fluid attempts to position itself as close to the power coils as possible. This, in effect, results in suspending the inertial body in the approximate geometric center of the housing. When a force is applied to the accelerometer (or to whatever device the accelerometer is mounted on), so as to cause angular or linear acceleration, the inertial body attempts to remain in place. The inertial body therefore “presses” against the magnetic fluid, disturbing it and changing the distribution of the magnetic fields inside the magnetic fluid. This change in the magnetic field distribution is sensed by the measuring coils, and is then converted electronically to values of linear and angular acceleration. Knowing linear and angular acceleration, it is then possible, through straightforward mathematical operations, to calculate linear and angular velocity, and, if necessary, linear and angular position. Phrased another way, the accelerometer provides information about six degrees of freedom—three linear degrees of freedom (x, y, z), and three angular (or rotational) degrees of freedom (αx, αy, αz).
One of the disadvantages described in an accelerometer such as that described in pending application Ser. No. 10/980,791, is the use of magnetic sensors to indirectly measure the change in position of the inertial body. Such magnetic sensors may be, for example, inductive coils. Two such inductive coils are usually necessary to be positioned on each face of the “cube” of the sensors shown in pending application Ser. No. 10/980,791, if both linear and angular acceleration in all six degrees of freedom needs to be measured. The disadvantages of using such inductive sensors involve restrictions on the dimensions of the overall structure, bandwidth limitations due to the size and inductance of the sensing coils themselves. The manufacturability issue is of significant concern if mass production of the sensors is at issue. Miniaturization of the sensing coils can only be done up to a point, even if the finest gauge wire is used. After the sensing coils themselves are wound, further assembly and tweaking of the overall structure may be required. Also, additional calibration may be required, due to the non-uniformities involved in the manufacturing of the sensing coils.
Accordingly, there is a need in the art for an accelerometer that uses magneto-fluidic principles to suspend an inertial body, but avoids the use of magnetic sensors to detect the changes in position of the inertial body.